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In this paper, the trade-off between the target variables tomogram quality and reconstruction time of an implementation of Katsevich's exact reconstruction algorithm for helical cone-beam computed tomography (CT) is analyzed. This is accomplished by means of an OpenCL-based, parallel and portable realization of Katsevich's algorithm. The detailed examination is carried out on a phantom object which is composed of cubes with different attenuation coefficients. For this phantom object, X-ray cone-beam projections are simulated with different helix trajectory parameters. From the simulated projection data sets 3D tomograms are reconstructed. The impacts of the helix parameters on the tomogram quality and the reconstruction time are measured. Moreover, the speedup in dependence of the number of computing units on the OpenCL device is examined. To sum up the results: the tomogram quality increases monotonically with ascending number of projections while keeping the helix pitch fixed. A linear relationship between the overall runtime and the number of projections exists. The trade-off analysis between the tomogram quality and the reconstruction time proves that an optimum is reached if the criteria for the lateral and vertical sampling of the 3D space are fulfilled.